This invention relates to a cutter assembly consisting of a cutter bit and a holder in which the cutter bit is rotatably mounted.
Cutter assemblies of this type are extensively utilized on continuous mining machines and to a lesser extent on rotary auger drills, ditching machines and land-breakers.
Rotation of the cutter bits in all assemblies presently available on the market is accomplished by combining a skew angle with the angle of attack such that the cutter bit drags through a formation. The movement of the cutter bit through the formation causes an unbalanced moment on the cutter bit about its longitudinal axis, resulting in rotation of the cutter bit. In comparatively dry, clean areas, this unbalanced moment is sufficient to cause rotation of the cutter bit. However, in many cases, cuttings lodge between the bearing surfaces of the cutter and the holder, creating a frictional force which exceeds the unbalanced moment on the cutter bit tending to cause rotation. In such cases the cutter bit drags over the formation without rotating and the cutter bit body wears rapidly until the hard-metal insert of the cutter bit falls out and the bit must be replaced.